I'm incubating Aylesbury duck eggs for the first time. 5 out of 12 are still viable today (day 14). All the eggs had large air sacs on candling on day 1 after they arrived by post (ebay). The average weight of the 5 good eggs has reduced by the right percentage over the past 14 days with a humidity of 45% in an R-Com incubator. The air sacs are already about a quarter of the size of the egg. I would very much appreciate knowing what I should do about the humidity. Should I go by the size of the air sac or is the reduction in the weight of the eggs more important?

Thanks. My conclusion is that air sac size is probably more important than egg weight if you don't know how fresh the eggs are.

Only 2 ducklings hatched, both on day 27. The other three died in their shells between days 24 to 26. Over the course of the incubation period these three eggs lost 12.8% of their original weight on average by day 24. The two successful eggs lost 9.2% of their original weight by day 24. All had large air sacs, at least a third of the size of the egg.

It's difficult to say from such a small sample, but it seems to me that the eggs lost too much moisture before incubation started. My guess is that they can't have been that fresh to start with and so they had large air sacs from day 1. All 12 eggs on day 1 had an average weight of 79g which seems low for Aylesbury duck eggs.

One of the ducklings is doing really well, the other is very small compared with the first, but is eating and drinking. It's small size may be because it lost too much moisture during incubation.